1. Field of the Invention
The present invention relates to an image projection system, and more particularly, to an image projection system having multiple color light sources.
2. Description of the Related Arts
Multimedia projectors usually use an ultra high performance lamp (UHP lamp) as a light source. The UHP lamp has advantages of high efficient and high luminance, which has good performance in the light flux of the projectors. However, the UHP has a very high energy consumption is very huge, which in turn generates a great amount of heat. The lifetime of the UHP lamp is often effected by the huge and intense heat and is thus short (about 1,000-3,000 Hours) so that it needs frequent maintenance and replacement. In addition, and the UHP lamp is so expensive that the overall cost of the projector is largely increased. Further, the UHP lamp is a white light source, and thus, the projector needs an additional color filter to decompose the white light into primary color lights in order to process chromatic signals. If the distribution of the white light in the color spectrum does not meet the requirement of the color balance, the projector has to restrain the high-luminance primary color light. This leads to a low efficiency of light utilization.
The current trends for the projector is “thinner, smarter, and smaller”, with reduced amount of heat generated in order to improve the efficiency and the reliability. Light-emitting diodes (LEDs) are gaining advantages over the UHP as the main stream of light source for the projectors due to reduced amount of heat generation, low costs, and extended service life. Compared with the UHP lamps, the LED is much thinner and smaller than the UHP lamps, and the energy consumption of the LED is much lower. In addition, the LED is so endurable (more than 20,000 hours) that there is nearly no need for maintenance and replacement, and the light wave is adjustable.
However, the conventional projectors using LEDs as light sources surfer drawbacks of color shifting. The conventional projector uses three single primary color LEDs to generate primary color lights, which are then composed together to form chromatic images with a light-combining element. However, the LEDs of different colors have different luminance. The luminance of the red LED is usually larger than that of the green LED, and the luminance of the blue LED is the least. This causes problems of color shifting. Thus, the projector has to set light valve elements to adjust the luminance of the red LED and the green LED, which lows down the efficiency of light utilization.
Referring to FIG. 2 of the attached drawings, a conventional projector that employs LEDs as light sources is shown. The projector has a blue LED 102, a green LED 104, a red LED 106, an x-cube 108, and a projector lens 110. Each LED 102, 104, 106 emits a corresponding primary color light. The blue LED 102 emits a blue light (Bi); the green LED 104 emits a green light (Gi); and the red LED 106 emits a red light (Ri). These color lights propagate into the x-cube 108, which combines the color lights into chromatic images. As the luminance of the three LEDs is different from each other, the chromatic images generated by such a projector often suffer color unbalance.
Hence, an improved image projection system is required to overcome the disadvantages of the prior art.